The "nipple guys" are at it again. That is, Dr. William Goldberg and Mark Leyner, authors of the new medical trivia book, "Why Do Men Fall Asleep After Sex: More Questions You'd Only Ask a Doctor After Your Third Whiskey Sour." It's a sequel to their best-seller, "Why Do Men Have Nipples?," which answered hundreds of questions about bodily functions, inexplicable hair growth and, of course, mammary glands.

Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

The unexpected success of "Nipples," a unrestrained blend of the humorous and the factual, convinced Leyner and Goldberg that they'd barely scratched the surface of the profound curiosity people have about our smelly, noisy and often embarrassing bodies. This time around they explore the differences between men and women with 184 new questions.

In an interview with MSNBC.com, Leyner, a satirist and script writer, and Goldberg, an emergency medicine physician at a New York City hospital, discuss the battle of the sexes, why people are so captivated by our bizarre biology and their different styles of research. Leyner and Goldberg appear on The Body Odd, a bi-weekly MSNBC podcast.

Q. Why did you do a sequel to "Why Do Men Have Nipples?"

Dr. Billy: Are you serious? We thought we could make the world a better place.

Mark: We thought we could make our world a better place is more accurate. We also had an enormous amount of fun doing [the first book.] The wonderful thing about it is, it seems to give people an enormous amount of pleasure. We had the idea that we could do another one that could be even better. We found out that we'd barely scratched the surface.

Q. Judging from the title "Why Do Men Fall Asleep After Sex?," the new book is set up as a battle of the sexes. How far do you delve into the differences between men and women?

There are questions that are very prevalent and nagging that people are endlessly fascinated about. The differences between men and women — as much as people try to minimize it — there are marked physiological and biological differences between men and women from the moment of conception. And, as much as our society becomes more homogenous, there’s an even more interesting contra-distinction between men and women the more we try to be alike. It’s an issue that will never die.

Dr. Billy: When you write a book “Why Do Men Have Nipples?,” it rings of being exclusively male, which the first book wasn’t. We looked for a “why do women…” question, but there wasn’t something that was that catchy. We realized that we wanted it to be all inclusive. These are all these questions that nag both men and women

Q. Are men and women interested in different topics?

Dr. Billy: I don’t think so. Are men interested in the question, "is douching dangerous?" Ostensibly, no. But then you see the question is so ridiculous, you become fascinated by it.

Mark: There are things that men are supposed to be more interested in. The cliché that men are more interested in bathroom humor and sexual questions. Women are more interested in questions that have to do with emotional dynamics of men and women. One of the purposes of our book is to enable people to shamelessly shed their expectations about what they’re allowed to ask. You’ll probably find women going straight to the bathroom and sex stuff and men looking at other humorous things. That’s the raison d'être of the book— people can do what they like and not have to feel abashed about it or follow the dictates of convention as much.

Dr. Billy: Nothing is off-limits. We hope that men don’t just read the sports chapter or women just read the pregnancy chapter. There are questions on both sides that people will be fascinated by. In the chapter on pregnancy there’s the question, “Can you breastfeed with fake boobs?” I think a lot of people will think, “I never thought about that.”

Q. Why are people so fascinated by the odd and weird?

Dr. Billy: We spend every moment walking around in this incredibly well-constructed but hard-to-figure-out machine that is our bodies. Everything we do — when we think, when we hear, when we smell, when we eat — there are these processes that are happening that we don’t understand. You can’t escape from having these moments thinking, “how does it work?”

Mark: In order to navigate ourselves through our lives, we pretend that we can actually have control over things, some control over our destinies and control over our days and control over how we look and control how we age.

There’s such an imposed false sense of control. I think people are fascinated with what is much more unpredictable and full of accidents and full of extremes and full of physical attributes that don’t fit the norm of what’s beautiful, and full of physiological phenomenon that don’t fit the normal way that we should digest food or feel after we work out. There’s such a wild disarray and wild miscellany of human behavior and biological makeup and sexuality...

Dr. Billy: You love that word miscellany.

Mark: People are fascinated with what seem like extremes and oddities that feel like accidents, because it really is the true texture of human experience, as opposed to what we try to construct for ourselves that is more consoling through predictability.

Mark: When we do radio shows people will call up with very serious questions about things that are happening to them. It’s bracing because we’re doing a book that is, first and foremost, very entertaining. But it’s about real things and we have an affect on the audience which puts them at ease and makes them comfortable. It will provoke questions that are very poignant. People will call up with heartbreakingly real questions about what is happening to them. It really makes me realize that not only are we dealing with the frivolities of our bodies but also with the profound implications of mortality.

Dr. Billy: People will ask a question like "why do I sneeze when I look in the sun?" and I’ll think there’s no reason behind that. Then you look it up and there’s a real reason.

Mark: People would ask if it’s dangerous to hold in a fart, is it dangerous to hold in pee when you’re in a car — will you explode? People have a morbid fear of exploding. Thanks to our research in the first book, of all those things, holding in a sneeze turns out to be the one thing that can really be damaging.

Dr. Billy: Are you saying that because of our book people are sneezing and farting more?

Mark: People are certainly farting more.

Dr. Billy: We have made the world a more flatulent place. Mark and I tend to like different questions. Mark, for some reason this time around became obsessed with why do we have pubic hair. He went on this, would I call it a crusade?, to look into every reason. He was looking into pheromones and aardwolves and different animals and creatures he was researching and how they attract each other.

Mark: The fact that we only have hair on our bodies on places that seem like ...

Dr. Billy: See, I got him started, he’s going to go off on pubic hair again.

I like simple questions like, "can my baby be born with teeth?" It sounds like some horror film to have some little creature coming out with fangs. Turns out there’s this uncommon phenomenon where a kid can be born with natal teeth. A child can actually come out of the womb with a couple of small, not perfectly formed teeth. Two or three little teeth.

Mark: Can’t people develop tumors that have hair and teeth?

Dr. Billy: That is not uncommon. I’ve seen it several times. There are these dermoid cysts that people can have.

Mark: I had a friend who had a cyst removed and she called and said it had hair and teeth and I brought her a tiny little toothbrush to the hospital. I haven’t talked to her since.

Dr. Billy: They are just tumors made up of different cell lines. Teratomas.

Dr. Billy: We have a research lab in Chechnya.

Mark: That’s a time share.

Dr. Billy: And in Hoboken, N.J. and in Jackson Hole, Wyoming. We have teams of researchers like Oompa Loompas who comb the medical journals for us.

Mark: We both have fairly wonderful libraries. Then there’s the Internet.

Dr. Billy: I basically do it at the medical library. Nowadays, you can access all of that online. I search the medical journals for all of these questions. We want to start scientific and then simplify it.

Mark: Billy and I have profoundly different styles of research that when combined have turned out to be wonderfully delicious for people. Because of Billy's training, he is very good at getting to the heart of things and making something that’s very unmanageably complex, very apprehensible to someone. I have this way of going off on an endless, algorithmic series of tangents. When you combine both methods, you get “Why do men fall asleep after sex?”

Dr. Billy: We came across this really strange journal, Journal of the Chemical Senses. We look anywhere and everywhere to find the answers to these questions. And, ultimately, there are some questions that we don’t have answers to. People get very frustrated about that. But I think that’s beautiful. You don’t find the answer until you start asking the question.